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Re: Sam Barros' 5000Watts Car Ignition coil update: tests, and



to: Scott, Sam

Without overstressing the coil most are rated in the range of 130-150 mJ at
a working potential of 50 kV.  We use the Accel Supercoil for most HV pulse
triggering applications (our Marx generators).  We use a standard doubler on
the AC power line to run 339 VDC peak and fire at 15 pps.  They will last a
long time at this rating.  You could probably increase the energy to 250-300
mJ if the duty cycle is shorter -- 3-5 pps.

Regards,

Dr.Resonance-at-next-wave-dot-net


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, February 24, 1999 7:29 PM
Subject: Re: Sam Barros' 5000Watts Car Ignition coil update: tests, and


>Original Poster: Scott Stephens <Scott2-at-mediaone-dot-net>
>
>At 03:36 AM 2/22/99 -0700, you wrote:
>
>>Original Poster: Sam Barros <sambarros-at-yahoo-dot-com>
>
>> I am trying to calculate how much power, in theory, an ignition coil
>>would be able to handle. I suppose I would have to look into how much
>>current the wire can take, and than see if it is more, or less than
>>what it takes to saturate the core... Any ideas there? The wire on the
>>primary is 0.50mm diameter, about 240meters long, and oil-immersed.
>>The resistance of the windings is 3Ohms.
>
>I would consider the total resistance of the wire, core loss and thermal
>effects. I measured these for my car coils (search the archive for my data
&
>comments) by measuring the 3db tuning bandwidth, from which I derived the
>coil's Q, and from measuring reactance of the coil at the frequency in
>question, using signal generator and scope, I found the effective
resistance
>(both AC and DC resistance) of which the AC was significantly greater,
>probably due to the skin and magnetic parallel effects.
>
>After you know the resistance, you figure the average power dissapation. I
>then tried a crude thermal analysis. Using values of thermal conductivity &
>dissapation for paper, oil & epoxy I estimated the power to create around a
>200 degree C thermal gradient in the center of my car coil immersed in
>flowing oil (driven by a CPU cooling fan). The coil has a laminated paper
or
>epoxy - copper structure, so I could just SWAG or guestimate.
>
>I was dissapointed to calculate my coil couldn't handle over a few hundred
>watts dissapation without burning. That means if I couple the coil to a
>constant load, I could let the coil dissapate 200 Watts in heat while the
>load gets 600 watts. I could probably push the power to 1000 watts for 5 -
>10 second runs, then let it cool down for a while.
>
>I figured it would be good to somehow measure the resistance of the copper
>coil, using it as a thermistor, to let me know when I'd pushed it as far as
>I could go. I planned to run without a core, letting the car coil feed a
>capacitor, resonating around 8KHz. Search the archive for the rest. The
>core, being a solenoid, will saturate gradualy, and eat half of you power.
>
>>
>> Is this correct for the maximum theoretical output of an ignition
>>coil? And, if so, is di/dt given in Hz?
>>
>> V = L di/dt
>>Where:
>> V is the output voltage
>> L is the inductance in Henrys
>> di/dt is the rate of change of current flow as the field collapses in
>>the coil.
>
>Yes, but remember capacitance, which is very significant, will reduce that
>value greatly.
>
>> How about this for power output?
>>
>>P = (L di/dt)^2 / R
>>where P is the power in watts and R is the total resistance of the
>>coil secondary, the plug wire and the ionized spark gap.
>
>P=V^2/R is for direct current/time. It will work if you integrate (average)
>your pulse.
>P=I^2 * R too.
>
>You need to know Q (AC losses) core losses (which will depend on your power
>levels)
>
> Also, how
>>important is the inductance of such a coil in coildriver applications?
>
>>Did you all get it and didn't think it
>>was worth a comment or was there a problem while I tried to send the
>>file?
>
>You must be using the new file naming convention, it left blanks in the
file
>name which irritated me when I had to use Microsh*t's Windowz Explorer to
>rename & view.
>
>My 2 cents is the best coil will have the best thermal dissapation
>character. My TC efforts have stalled presently, when I was conteplating my
>own induction coil based on an Allied Metglass core, with teflon insulated
>windings, with forced convection oil immersed cooling. Being SCR pumped, Fo
>around 4KHz, and 100KV + output voltage.
>
>How practical capacitors and spark gaps will be at 100KV + potentials I
hope
>to find out.
>
>
>